If Scott Brown’s election three years ago convinced Massachusetts Republicans that anything was possible, his decision not to run in ­another Senate special election ­reminded them that it is not.

Decisions by Brown and numerous other top-tier Republicans to bow out of contention for a special US Senate election were made for individual reasons but reflect ­Republicans’ new reality, much like their pre-2010 reality: No one ­expects one of them to win.

“Of course, it’s a rare opportunity, and Brown showed in 2010 that it’s possible,” said GOP political consultant Jason Kauppi. “This special election, though, comes right after an enormous national election in which, at least in the Northeast, ­Republicans fared very badly.”

The Massachusetts GOP is trying to put the best face on the lesser-known Republican contenders who are stepping up, including state Representative Daniel B. Winslow, who announced his candidacy Thursday, and Cohasset private ­equity investor Gabriel E. Gomez, who is expected to become a candidate soon.

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But some Republican observers said the disinterest among more seasoned candidates suggests that candidates do not want to squander political capital on a race widely seen as an uphill battle.

“You’re looking at your chances of winning,” said Kauppi, who contrasted their odds with Brown’s ­upset in 2010. “He caught lightning in a bottle. Can you catch lightning in a bottle again? I just think the ­national atmospherics are not forecast to go Republicans’ way, let alone in Massachusetts.”

William F. Weld, Richard R. ­Tisei, Kerry Healey, and Charles D. Baker all declined to mount a campaign for US Senate, though each is believed to still have political aspirations.

GOP observers say that ­Baker wants to run for governor again and that ­Tisei, a former state senator who lost a hard-fought race for Congress in November, wants to try for that spot again. And though Weld, a former governor, or Healey, a former lieutenant governor, might want to return to politics, both have lost bruising elections and probably understand that this is not their ­moment, said GOP consultants.

“If you’ve been a successful ­Republican statewide candidate or political figure, like many of those who said no are, you’re aware that to win, you have to have the right candidate in the right race at the right time,” said Republican political consultant Rob Gray.

Until last week, Republicans had hoped that Brown still had enough cachet to reclaim the Senate seat that John F. Kerry vacated to ­become secretary of state. Brown’s reelection loss in November, though deflating, came in a huge-turnout presidential election to a Democratic rising star, ­Elizabeth Warren, and the GOP hoped the odds would return to his favor in ­another lower-turnout special election.

The Democrats already in the race, US Representatives Edward J. Markey and ­Stephen F. Lynch, have established voting bases in their districts, but neither has the national celebrity that Brown enjoyed after his Senate upset. And he seemed to be positioning himself for a run, by lobbying GOP activists to elect his ally, Kirsten Hughes, as the new chairman of the state party.

The timing of Brown’s decision not to run, late last week, made it even more likely that other potential candidates would also decline, Gray said. A candidate must collect 10,000 signatures from registered ­Republicans or unenrolled voters by Feb. 27 to qualify for the primary, according to the office of the secretary of the Common­wealth.

“If Brown had announced he wasn’t running in mid-January, we would have been more likely to ­attract better Republican candidates, because they have more time to maneuver, staff up, get the signatures,” Gray said. “It’s no small task and ­requires hiring people.”

Rather than trying to clear such a tall hurdle now, Gray said, the better-­known candidates would be more likely to seek a better position in 2014 or in the Senate reelections.

Nonetheless, some expressed opti­mism about the candidates who are emerging as candidates in the special Senate election. Kauppi pointed out that when Brown ­entered the US Senate race in 2009, he was a state legislator who was probably only as well known as Winslow is now.

“It’s just that the window is so short right now and people are getting overly anxious,” said Lisa ­Barstow, a Republican state committeewoman and a public relations strategist. “If we just took, as a party, a collective deep breath, we can pull this off. . . . These are not sacrificial lambs. Each and every one of them has a very viable chance against a Markey or a Lynch.”

Even lesser-known contenders began emerging this week: Jon Fetherston, who was chairman of the Board of Selectmen in Ashland and lost a race for the Legislature, announced his candidacy. Governor’s Councilor Jennie Caissie is ­also reportedly considering a run. Also viewed as potential contenders are state Senate minority leader Bruce E. Tarr and former US ­attorney Michael J. Sullivan.

The state GOP is contrasting the freshness of the emerging potential candidates with the familiarity of the Democratic field.

Tim Buckley, a party spokesmen, characterized Lynch and Markey as “two creatures of Washington, D.C., vying for the Senate.”

“The current group of ­Republicans taking a long, hard look at this race are going to be a stark contrast to the mediocre congressmen currently vying for the Democratic nomination,” Buckley said. “What better way to offer a fresh face and new direction for the voters of Massa­chusetts than with this group of potential candidates?”

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